The present invention relates generally to antennas, and more particularly to antennas used with wireless communications devices.
Radiotelephones generally refer to communications terminals which provide a wireless communications link to one or more other communications terminals. Radiotelephones may be used in a variety of different applications, including cellular telephone, land-mobile (e.g., police and fire departments), and satellite communications systems. Radiotelephones typically include an antenna for transmitting and/or receiving wireless communications signals. Historically, monopole and dipole antennas have been employed in various radiotelephone applications, due to their simplicity, wideband response, broad radiation pattern, and low cost.
However, radiotelephones and other wireless communications devices are undergoing miniaturization. Indeed, many contemporary radiotelephones are less than 11 centimeters in length. As a result, there is increasing interest in small antennas that can be utilized as internally-mounted antennas for radiotelephones.
In addition, it is becoming desirable for radiotelephones to be able to operate within multiple frequency bands in order to utilize more than one communications system. For example, GSM (Global System for Mobile) is a digital mobile telephone system that operates from 880 MHz to 960 MHz. DCS (Digital Communications System) is a digital mobile telephone system that operates from 1710 MHz to 1880 MHz. The frequency bands allocated for cellular AMPS (Advanced Mobile Phone Service) and D-AMPS (Digital Advanced Mobile Phone Service) in North America are 824-894 MHz and 1850-1990 MHz, respectively. Since there are two different frequency bands for these systems, radiotelephone service subscribers who travel over service areas employing different frequency bands may need two separate antennas unless a dual-frequency antenna is used.
In addition, radiotelephones may also incorporate Global Positioning System (GPS) technology and Bluetooth wireless technology. GPS is a constellation of spaced-apart satellites that orbit the Earth and make it possible for people with ground receivers to pinpoint their geographic location. Bluetooth technology provides a universal radio interface in the 2.45 GHz frequency band that enables portable electronic devices to connect and communicate wirelessly via short-range ad hoc networks. Accordingly, radiotelephones incorporating these technologies may require additional antennas tuned for the particular frequencies of GPS and Bluetooth.
Inverted-F antennas are designed to fit within the confines of radiotelephones, particularly radiotelephones undergoing miniaturization. As is well known to those having skill in the art, inverted-F antennas typically include a linear (i.e., straight) conductive element that is maintained in spaced apart relationship with a ground plane. Examples of inverted-F antennas are described in U.S. Pat. Nos. 5,684,492 and 5,434,579 which are incorporated herein by reference in their entirety.
Conventional inverted-F antennas, by design, resonate within a narrow frequency band, as compared with other types of antennas, such as helices, monopoles and dipoles. In addition, conventional inverted-F antennas are typically large. Lumped elements can be used to match a smaller non-resonant antenna to an RF circuit. Unfortunately, such an antenna may be narrow band and the lumped elements may introduce additional losses in the overall transmitted/received signal, may take up circuit board space, and may add to manufacturing costs.
Unfortunately, it may be unrealistic to incorporate multiple antennas within a radiotelephone for aesthetic reasons as well as for space-constraint reasons. In addition, some way of isolating multiple antennas operating simultaneously in close proximity within a radiotelephone may also be necessary. As such, a need exists for small, internal radiotelephone antennas that can operate within multiple frequency bands.
In view of the above discussion, the present invention can provide compact antennas that can radiate within multiple frequency bands for use within wireless communications devices, such as radiotelephones. An antenna according to an embodiment of the present invention may include first and second conductive branches in adjacent, spaced-apart, mirror-image relationship. The first conductive branch may include first and second signal feeds extending therefrom, and the second conductive branch may include third and fourth signal feeds extending therefrom.
The first and second signal feeds terminate at respective first and second switches, such as micro-electromechanical systems (MEMS) switches. The first switch is configured to selectively connect the first signal feed to a receiver and/or a transmitter that receives and/or transmits wireless communications signals, or to maintain the first signal feed in an open circuit (i.e., the first switch can be open). The second switch is configured to selectively connect the second signal feed to the same or a different receiver and/or transmitter, or to ground, or to maintain the second signal feed in an open circuit (i.e., the second switch can be open).
The third and fourth feeds terminate at respective third and fourth switches, such as MEMS switches. The third switch is configured to selectively connect the third feed to the same or a different receiver and/or transmitter, or to ground, or to maintain the third feed in an open circuit (i.e., the third switch can be open). The fourth switch is configured to selectively connect the fourth feed to the same or a different receiver and/or transmitter, or to maintain the fourth feed in an open circuit (i.e., the fourth switch can be open).
The first and second conductive branches can jointly radiate as a dipole antenna in a first frequency band when the first and fourth switches are open, and when the second and third switches electrically connect the second and third feeds to a first receiver. The first conductive branch can radiate as an inverted-F antenna in a second frequency band different from the first frequency band when the third and fourth switches are open, when the first switch is electrically connected to a second receiver, and when the second switch is electrically connected to ground. In addition, the first or second conductive branches can radiate independently as separate monopole antennas.
The first and second conductive branches can also radiate as separate inverted-F antennas in respective different frequency bands. For example, the first conductive branch can radiate as an inverted-F antenna when the first switch is electrically connected to a receiver, and when the second switch is electrically connected to ground. The second conductive branch can radiate as an inverted-F antenna when the third switch is electrically connected to ground, and when the fourth switch is electrically connected to a different receiver.
Antennas according to the present invention may be used with multiple receivers and/or transmitters, and multiple combinations of receivers and/or transmitters. Exemplary receivers and/or transmitters may include, but are not limited to, AMPS receivers/transmitters, PCS receivers/transmitters, GSM receivers/transmitters, DCS receivers/transmitters, GPS receivers, and Bluetooth receivers. For example, when the first and second conductive branches jointly radiate as a dipole antenna, the second and third switches may electrically connect the second and third feeds to a GSM transceiver. When the antenna structure is changed by reconfiguring the various switches as described above, the first and second conductive branches may be electrically connected to different receivers/transmitters. For example, the first conductive branch may radiate as an inverted-F antenna for a GPS receiver and the second conductive branch may radiate as an inverted-F antenna for a Bluetooth receiver.
According to additional embodiments of the present invention, portions (or all) of the first and second conductive branches may be disposed on or within one or more dielectric substrates. In addition, antennas according to the present invention may include first and second conductive branches with different configurations and with different effective electrical lengths.
Antennas according to the present invention may be particularly well suited for use within a variety of communications systems utilizing different frequency bands. Furthermore, because of their compact size, antennas according to the present invention may be easily incorporated within small communications devices. Furthermore, antennas according to the present invention may be well suited for use with receive-only applications such as GPS.